1. Field of the Invention
The present invention relates to the secure distribution of digital content and more particularly to a key management and exchange mechanism for copy protection of digital content provided on Digital Video Disc (DVD).
2. Background
Rapid advances in recording and playback technology have led from analog video cassette tapes and video cassette tape players, to digitized video available on optical disks. Digitized video on optical disks is typically referred to as being in compact disk (CD) format. Digital video can be played back on a television with the aid of special hardware, or played back on the video display device of a general purpose computer such as a personal computer (PC). Digitized video is typically compressed so that the available data storage capacity of the CD is used most efficiently. Several schemes for compression and decompression of digitized video have been adopted for use in industry such as the Indeo.RTM. format developed by Intel Corp., of Santa Clara, Calif., and the family of MPEG specifications for video/audio compression and decompression developed by committee of the International Standards Organization (ISO).
Even with the various compression techniques that are available, it has not been possible to record full-length motion pictures on CDs. However, a new recording format for optical disks has been developed that makes it possible to store a full-length motion picture encoded as compressed digital information. DVDs are optical disks having compressed video (and audio) data recorded thereon in this new format.
The development of DVD technology has led to a substantial interest in the computer and entertainment industries in incorporating video data into multimedia and related applications for use in home entertainment equipment such as consumer players, as well as in personal computers. Potential growth in this area has been triggered by DVD technology because the storage capacity offered by the DVD format enables placing a typical full-length motion picture, in its entirety, on a single disc.
With the compressed data of an entire movie readily available in a single disc, content providers are extremely concerned with the possibility of unauthorized copying of the content. In view of this challenge, various schemes for achieving copy protection, including but not limited to encryption of the content have been proposed.
FIGS. 1(a)-1(b) illustrate the vulnerability of content to observation and unauthorized copying.
FIG. 1(a) shows a DVD playback system 100 in which a DVD drive 102, reads a DVD disc 103 to produce MPEG coded YUV data 104 as an output. DVD drive 102 is coupled to an MPEG decoder 106 so as to communicate MPEG coded YUV data 104 from DVD drive 102 to MPEG decoder 106. MPEG decoder 106 operates on MPEG coded YUV data 104 so as to produce decompressed YUV data 108 as an output. MPEG decoder 106 is coupled to a video controller 110 so as to communicate YUV data 108 from MPEG decoder 106 to video controller 110. Video controller 110 operates on YUV data 108 to produce analog video 112 as an output. Video controller 110 is coupled to a display 114 so as to communicate analog video 112 from video controller 110 to display 114. In this configuration, MPEG coded YUV data 104, YUV data 108, and analog video 112 are all unencrypted and susceptible to unauthorized copying.
As illustrated in FIG. 1(b), even encrypting the MPEG coded YUV data does not solve the problem. In FIG. 1(b) a DVD playback system 150 is shown in which a DVD drive 152, reads a DVD disc 153 to produce encrypted MPEG coded YUV data 154 as an output. DVD drive 152 is coupled to a decryptor 156 so as to communicate encrypted MPEG coded YUV data 154 from DVD drive 152 to decryptor 156. Decryptor 156 operates on encrypted MPEG data 154 to produce MPEG coded YUV data 158 as an output. The MPEG coded YUV data output of decryptor 156 is communicated to an MPEG decoder 160. MPEG decoder 160 operates on MPEG coded YUV data 158 so as to produce decompressed YUV data 162 as an output. MPEG decoder 160 is coupled to a video controller 164 so as to communicate YUV data 162 from MPEG decoder 160 to video controller 164. Video controller 164 operates on YUV data 162 to produce analog video 166 as an output. Video controller 164 is coupled to a display 168 so as to communicate analog video 166 from video controller 164 to display 168. In this configuration, MPEG coded YUV data 158, YUV data 162, and analog video 166 are all unencrypted and susceptible to unauthorized copying.
Currently, all proposed encryption schemes for DVD copy protection use global secrets. An example of a copy protection scheme which uses a global secret is one that uses one or more non-keyed algorithms to either disrupt analog gain control or directly invert the luminance in a YUV data frame. All non-keyed transforms have what is effectively a global secret, i.e., knowledge of the algorithm employed by the transform. Once that algorithm is known then the entire system is compromised. This should be contrasted with cryptography which assumes that an adversary has knowledge of the algorithm and the output but does not know the key of the transform. As long as the key remains secret then the transform is secure. In most cryptographic systems key management becomes the central issue.
What is needed is a system and method for receiving compressed, encrypted YUV data and decompressing and decrypting that YUV data without exposing decrypted data or cryptographic keys to observation.